Ancient Megadroughts in American Southwest Area a Snapshot of Area's Dry Future

The arid southwest is dry, but not as dry as it was during megadroughts that lasted thousands of years when the planet's temperature was at, or just above, its current level. Scientists believe that studying the records of these long-lasting droughts could provide clues to what our future will be like in a warmer world. It's not as if the southwest has much water to spare in the first place. The exploded populations in Nevada, Arizona, New Mexico and southern California already present a massive burden on water supplies from aquifers and the Colorado river. But Reuters reports that scientists confirm millennial droughts occurred in the southwest during periods when Earth's annual temperature was the same as, or just a touch higher, than today's average temperatures -- and that as the global temperature climbs, droughts in this area are going to lengthen.

"These findings tally with projections by the U.N. Intergovernmental Panel on Climate Change and others, according to study author Peter Fawcett of the University of New Mexico. The results were published in the current edition of Nature."

The article's abstract states, "The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern... Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT."

By analyzing samples from Valles Caldera, a dried lake in New Mexico, the researchers found that drought tolerant plant communities collapse during these intervals, and summer precipitation drops significantly. Also, when comparing climate records, "in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase."

Instead, it's entering a hotter, drier phase.

"The IPCC model suggests that when you warm the climate, you'll see extended droughts in this part of the world and this is what the paleo record seems to be telling us," Fawcett said in a telephone interview with Reuters. "When you've got past temperatures that were at or above today's conditions, conditions got drier."

As droughts last longer, and water becomes even more scarce, how exactly will the residents of the southwest cope? It's an ominous question.

A hike in water prices could mean costs in the trillions of dollars to provide water to residents. And that's if additional water can be found to provide to residents. As adaptation gets even more expensive, we could see people moving out of the southwest as fast as they moved in decades ago.